1. Field of the Invention
The present invention relates to a method for recording an image using a solution containing an aqueous dye and electrochemically depositing the dye to form the image, and an image recording apparatus suitable for the method.
2. Description of the Related Art
Many methods of using a liquid image forming material are known in image recording technologies used in offices. For example, silver salt recording technology, ink jet recording technology, and electrophotographic recording technology.
Printing technology using silver salt has been published in Tanemura Hatsumi et al., "HIGH QUALITY COLOR COPYING SYSTEM USING THE SILVER SALT PHOTOGRAPHIC METHOD", Advance in Japan Hardcopy '89, Research Publication, p229. Printing technology using liquid development electrophotographic technology has been published in E. B. Caruthers, et al., "Modeling of Liquid Toner Electrical Characteristics" Proceedings of IS & T 10th Int'l. Congress on Advances in Non-Impact Printing Technologies, p204 ('94). Printing technology using ink jet recording has been published in many technical reports such as Usui Minoru "Developments in New-system MACH" Advance in Japan Hardcopy '96, Research Publication, p161.
Regarding conventional technologies closely related to the present invention, there are also published, for example Japanese Patent Application Laid-Open (JP-A) No. 7-181750 or Japanese Patent Application Laid-Open (JP-A) No. 62-267767, wherein there is used an electrodeposition liquid in which a dye is dispersed in a liquid insulator to generate an electrical double layer., JP-A No. 4-9902, "Fine Pattern Forming Method" relating to an electrodeposition printing technology using a printing plate having an insulated pattern on an electrically conductive substrate, and JP-A No. 6-293125, "Electrodeposition Offset Printing Method and Printing Plate".
Further, there is also an electrolytic developing method as one conventional technology. For example, such a method is disclosed in The Society of Electrophotography of Japan, Research Discussion Proceedings, p32 (1971) and p24 (1964, 11). The electrolytic development method comprises reducing zinc oxide by application of a voltage of 10 V or higher, with simultaneous exposure to light. The electrons thus generated are shifted to a dissolved dye precursor to reduce the precursor, and color-developing and depositing on the surface of the reduced zinc film are carried out, thereby forming an image. This is different in the recording method.
Properties required for printing technology used in an office are, for example, a high color image quality of 600 DPI (dots per inch) or higher and multi-gradation, capability of printing on plain paper, image fastness as high as possible according to the printing method, a high degree of safety of the recorded matter and recording apparatus, as little waste as possible, and low running costs. However, the above-mentioned conventional technology cannot satisfy these requirements completely.
The recording method using silver salt, which is one of the conventional printing technologies, does not have problems of image quality or image fastness, but has a problem of its use at an office being inappropriate because of the use and disposal of chemically-active agent resulting from the chemical reaction associated with the printing process. Ink jet printing technology at high resolutions has the problem of compatibility between the realization of a nozzle having a small size and printing reliability. Electrophotographic technology does not have any problems with image quality, capability of printing on plain paper, or image fastness as high as can be gained according to the printing method, but has the following problems. That is, a large amount of energy is consumed in the fixing unit in an electrophotographic apparatus and the printing process thereof is complicated so that the size of the apparatus is large and safety and reliability problems arise.
In order to obtain an image having a high quality (resolution of a level of 1000 DPI, good color-reproduction, and multi-gradation) , the thickness of the image structure is preferably 2 microns or less, and more preferably 1 micron or less, in the light of the relationship between the range of color reproduction and sharpness of the image. Thus, the average particle size of the image forming material, which is a factor having an influence on the structure of the image, needs to be of a sub-micron order. However, when the average particle size of the image forming material is 5 microns or less, practical use of a powdery image forming material is difficult due to problems with the fluidity. In comparison, from this viewpoint, use of a liquid image forming material would be efficient. In the step of forming an image having a size of the order of several microns, from a technical point of view, highly accurate control of the pixel shapes is difficult within the minute range of the image forming material particles. Accordingly, from the viewpoint of controlling the coloring material accurately, it is considered to be a very effective method to use an aqueous dye solution having a molecular order size, i.e., the minimum particle size, as an electrodeposition material.
In the electrophotographic method using a liquid insulator developer disclosed in, for example JP-A No. 7-181750, the particle size of the image forming material is of a sub-micron order. As a result, high resolution can be realized, with high adaptability to record on plain paper. However, in this method a hydrocarbon solvent is used as a developer, thereby resulting in the serious problem of the safety of the vaporized gas of the solvent. Therefore the use of such a developer is severely restricted in certain nations.
In electrodeposition printing technology using a printing plate on which an insulator pattern is arranged on an electrically conductive substrate, as disclosed in JP-A No. 4-9902, complicated steps are necessary, for example the step of forming a non-image portion of an insulator resist beforehand by photolithography. As a result, it is difficult to change the image pattern for printing an image, at every printing. Furthermore, precision in the apparatus to be used is high, the apparatus is large in size, and many steps are necessary. Much waste is also generated. Therefore this method is used only when the apparatus is installed at a factory wherein satisfactory facilities are arranged and the printing operation is carried out therein. Additionally, the histeresis of the image forming step is liable to remain on the printing plate, so that capability of reproducing fine images is low. Moreover, image forming portions are concave, and consequently stick-selectivity of particles to the image forming portions by electrophoresis is weak and much liquid of the image forming material is liable to remain on these image forming portions, so that the viscosity of the image forming material is also weak. As a result, flow of the image forming material on the image forming portions and break of condensation of the material are easily caused, in the transferring step. This makes it difficult to obtain a high quality image.
As described above, the conventional image forming methods have not been able to satisfy the requirements for the recording method used in an office safely and with a simple apparatus.
In order to provide an image with high image quality (1000 DPI or higher and multi-gradation), it is necessary to use a liquid image forming material containing a fine particle dye, whose particle size is preferably 1 micrometer or smaller. Considering the installation of the apparatus at an office, the liquid used for the image forming material needs to have a high degree of safety, such as water. Since it is necessary for the recording method used at an office to easily prepare various sorts of recorded matters in small amounts and at low cost, any printing method using a printing plate which cannot be recycled is inappropriate. Therefore, in the commercial market, preferred is a recording system of inputting an image signal to make image information every recording process and, in outputting print information, transferring the image forming material in an image pattern onto a recording medium corresponding to a user's needs, such as plain paper, thereby performing recording.